It is known to electroplate the surfaces of semiconductor wafers. It has been difficult, however, to obtain an electroplated layer of uniform thickness. It has been especially difficult to achieve the desired thickness uniformity at a high rate of metal deposition. Known systems for electroplating semiconductor products are described in U.S. Pat. Nos. 5,833,820 (Dubin), 5,670,034 (Lowery), 5,472,592 (Lowery), and 5,421,987 (Tzanavaras).